Method and device for facilitating the insertion of a coiled tube into a well and for loosening stuck objects in a well

ABSTRACT

Method for overcoming friction between a coiled tube and the wall of a well by an oil- or gas well, and for enabling application of impact energy to loosen stuck objects in a well. Pressure changes are applied to a liquid flowing in the coiled tube by periodically shutting off the liquid flow at or near the outlet of the coiled tube. Pressure changes, pressure strokes, are applied by means of a valve device comprising a valve body ( 31 ) arranged to seal against a valve seat ( 45 ) and to shut off the liquid flow whenever the flow rate exceeds a predetermined value, and to remain shut until the pressure in the liquid upstream of the valve body ( 31 ) is lower than a predetermined value, and that the valve body ( 31 ) has a slide ( 3 ) arranged thereto, which is arranged to open for a liquid flow past the valve body ( 31 ), to reduce, thereby, the pressure in the liquid upstream of the valve body ( 31 ) whenever the pressure in the liquid upstream of the valve body ( 31 ) exceeds a predetermined value. A damping device in which pistons in the form of collars ( 25, 26 ), channels ( 27, 28 ) and check valves ( 29, 30 ) are moved in annular spaces ( 17, 18, 19 ) filled with liquid, contributes to the valve device being closed long enough for a pressure rise to spread in the liquid in the coiled tube, and being open long enough for full liquid flow to be established before the next shut-off.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to PCT Application No. PCT/NO97/00147filed Jun. 6, 1997 which claims priority from Norwegian PatentApplication No. 962429 filed Jun. 6, 1996.

BACKGROUND OF THE INVENTION

The invention relates to a method and a device for facilitating theinsertion of a coiled tube into an oil or gas well, and for applying ofimpact energy to stuck objects in an oil or gas well.

On inserting a coiled tube into an oil or gas well, in the followingreferred to as a well, the length of insertion is limited by frictionbetween the coiled tube and the wall of the well. Even if the coiledtube is straightened in a separate straightening apparatus before beingintroduced into the well, it will adopt the form of a wave or a helix inthe well. As the coiled tube is being pushed further and further downthe well, and there are more points of contact between the coiled tubeand the wall of the well, the total friction increases to a level atwhich the end of the coiled tube does not proceed further into the well.Further supply of coiled tube only leads to more turns being formed inthe helix adopted by the coiled tube.

As is quite natural, the problem arises especially in wells of longhorizontal stretches, in which weights at the end of the coiled tubewill not contribute to stretching out the coiled tube.

It is known to mount a remotely controlled, motor driven propulsiondevice, a well tractor, at the end of the coiled tube to draw the coiledtube into the well. A well tractor is expensive and complex, andoperational disturbances may easily occur. Furthermore, it is difficultto construct well tractors which are able to proceed and providesufficient force in wells of small cross-sections. The cross-section isalways smallest at the innermost/downmost part of a well, and long wellsmay also have the smallest cross-sections.

Objects that are stuck in a well, are most commonly loosened by applyingimpact energy to them. An impact tool which has been arranged to a drillstring or a coiled tube, is inserted down to the stuck object and isactivated. Known impact tools use a pre-tensioned spring whichaccelerates a mass, a hammer, which after having achieved appropriatespeed, strikes against a stop transferring impact energy to the stuckobject. Before each stroke the spring is tensioned by means of ahydraulic mechanism which is activated by a pressure liquid in the drillstring or the coiled tube. The spring energy is released when thepre-tensioning has reached a predetermined value. A drawback of thisknown solution is that very powerful and space-consuming springs have tobe provided to achieve the required impact energy. Another known type ofimpact tool is periodically extended and lifts the drill string orcoiled tube which is above the impact tool, and then lets the drillstring or coiled tube drop again, so that the mass of the drill stringor the coiled tube causes a hammer effect. This type of impact tool hasthe unfavourable effect that impacts are transferred to the hole drillstring or coiled tube in such a way that the couplings and otherequipment arranged thereto, may be damaged.

The object of the invention is to provide a method and a simple,inexpensive device for facilitating the insertion of a coiled tube intoa well, and for applying impact energy to objects which are stuck in awell. The aim is reached through features as indicated in the followingdescription and subsequent claims.

According to the invention the aim is reached through applying impactchanges or pressure strokes to a liquid flowing through a coiled tube ordrill string. A pressure stroke in a coiled tube will contribute tobriefly overcoming frictional forces between a coiled tube and the wallof the well, so that the coiled tube may be introduced a little furtherinto the well by each pressure stroke.

Pressure strokes may be transferred to a stuck object by the coiled tubeor drill string in a known manner being lead into contact with, andpossibly attached to, the stuck object. Pressure strokes may also beused to accelerate a mass, a hammer, which in a manner known in itself,strikes against a stop which transfers impact energy to the stuckobject.

Pressure strokes is achieved, according to the invention, by periodicalshut-off of a liquid flow in the coiled tube or drill string, a valvedevice being located at or near the outlet of the coiled spring. Thevalve device may advantageously be such, that it is activated once theliquid flow exceeds a predetermined flow rate. Then it is possible tocarry out ordinary well operations by a lower and normal flow rate, andif a need for pressure changes arises, the flow rate is increased toactivate the valve device.

To achieve the best possible effect, the valve device should be such,that after having shut off, it remains shut long enough for the pressurerise to spread in the liquid, and so that after having opened, itremains open long enough to re-establish full flow rate.

BRIEF DESCRIPTION OF THE DRAWINGS

An embodiment of a preferred valve device for the periodical shut-off ofthe liquid flow in a coiled tube or a drill string is described in thefollowing with reference to the accompanying drawings, in which

FIG. 1 schematically shows a sectional side view of a part of a valvedevice in its opened starting position;

FIG. 2 shows the valve devised in closed position;

FIG. 3 shows the valve device as it is about to open and revert to itsstarting position;

FIG. 4 schematically shows a cross-section of the housing and valve bodyof the valve device;

FIG. 5 schematically shows a cross-section of a damping device.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

In FIG. 1 reference numeral 1 indicates a valve device which can openand close periodically for a liquid flow. The valve device 1 which isshown in vertical position, comprises an external tubular housing 2, inwhich are provided movable parts.

Before the invention is described further, it should be mentioned thatthe shown housing 2 and said movable parts are shown schematically. Thisprovides a clearly set out figure, and the way of working of theinvention will be easily understood. In practice, the housing 2 will bedivided into several parts which are typically joined up as a housing 2by means of threaded couplings which are made pressure tight by means ofseals. Shoulders and other items which in the figure appear as parts ofthe housing 2, may in practice be separate parts which in known mannerare secured inside the housing 2. Further, movable parts in the housing2 may in the same way be made up of several parts. The division isnecessary to enable production of the valve device in machine tools orother production equipment. Division is also necessary to enablemounting of movable parts in the housing 2. It is common that down-holetools have an external tubular housing, and that within the housing arearranged both fixed and movable parts. A skilled person will undertake adivision suitable for the equipment that he wants to use for theproduction, and at the same time take into account that the device shallbe mountable and dismountable.

The housing 2 is further shown without end couplings as such are wellknown from other down-hole equipment.

Inside the housing 2 is arranged an axially displaceable slide 3 whichat its lower end is provided externally with three separate annularseals 4, 5, 6 mentioned from the top downwards. A channel 7 in the slide3 ends at its bottom end in the lower end surface of the slide 3, and atthe top in a transverse hole in the slide 3, between the seals 4, 5.

The slide 3 is retained in an upper starting position by a pre-tensionedspring 9 which is supported by a first annular shoulder 10 inside thehousing 2, and works on the underside of an external shoulder 11 at theupper end of an axially displaceable cylindrical sleeve 12, which at itslower end is attached to the slide 3. The sleeve 12 is at its bottomprovided with openings 13, so that liquid can flow through the sleeve12. Below the shoulder 10 there is, inside the housing 2, a secondannular shoulder 14. The shoulders 10, 14 are provided with respectivelyseal 15 and 16, which are arranged to form a sliding tightening againstthe outer surface of the sleeve 12. The shoulders 10, 14 define an upperannular space 17, a central annular space 18 and a lower annular space19. At the central annular space 18 the housing 2 has a larger internaldiameter than the adjacent annular spaces 17 and 19. The housing 2 mayhave the same internal diameter at the annular space 17 as at theannular space 19.

Below the shoulder 14 there is in the annular space between the housing2 and the sleeve 12 an annular piston 20 with seals 21, 22 which resttighteningly against the housing 2 and the sleeve 12, respectively. Theunderside of the shoulder 14 and the top side of the piston 20 thusdefine a portion 23 of the annular space between the housing 2 and thesleeve 12. A channel 24 in the shoulder 14 connects the portion 23 ofthe annular space with the annular spaces 17, 18, 19 above the shoulder14.

The annular spaces 17, 18, 19 and 23 are filled with hydraulic oil oranother liquid. The underside of the piston 20 is exposed to the liquidwhich is conveyed by the valve device 1, and ensures that always thesame pressure prevails in the liquid in the annular spaces 17, 18, 19and 23 as in the rest of the valve device 1. The annular space 23 withthe piston 20 serves as a reservoir and a pressure accumulator for theannular spaces 17, 18, 19.

The sleeve 12 is externally provided with an upper collar 25 and a lowercollar 26 which are both located between the shoulders 10, 14. Thestroke length of the sleeve 12 is restricted by the collars 25, 26abutting the shoulders 10, 14. The diameter of the upper collar 25 isadapted to the diameter of the housing 2 at the upper annular space 17,and the diameter of the lower collar 26 is adapted to the diameter ofthe housing 2 at the lower annular space 19, so that there is littleclearance between the housing 2 and the collars 25, 26. The distancebetween the collars 25, 26 is such, that they may be brought, separatelyor simultaneously, into the central annular space 18 by displacing thesleeve 12 axially in the housing 2. When the collars 25, 26 are in theannular space 18, there will, due to the larger outer diameter of theannular space 18, be a greater clearance outwards towards the housing 2,than when the collars 25, 26 are in the annular spaces 17 and 19,respectively.

In each of the collars 25, 26 has been provided, in the form of arelatively narrow channel 27 and 28, respectively, or in another manner,a limited cross-section, by which liquid may flow through or past thecollars 25, 26 when these are moved within the annular space 17 and 19,respectively. In each of the collars 25, 26 is further arranged a checkvalve 29 and 30, respectively, of a larger cross-sections than thechannels 27, 28. The flow resistance past the collars 25, 26 thus becomedirection dependent when the collars 25, 26 are moved in the annularspace 17 and the annular space 19, respectively. In one direction liquidmay pass the collar 25 through both channel 27 and check valve 29, andthe flow resistance is small. In the opposite direction liquid may onlypass the collar 25 in a restricted cross-section provided by the channel27 and the clearance between the collar 25 and the housing 2. When thecollar 25 is in the annular space 17, this provides great flowresistance. This is correspondingly also the case for the collar 26 whenit is in the annular space 19.

The check valve 29 in the collar 25 is arranged to open for liquid fromthe upper side of the collar 25 to its underside. The check valve 30 isarranged opposite, to open for liquid from the underside of the collar26 to its upper side. If the sleeve 12 is displaced, this entails greatflow resistance for the one of the collars 25, 26 which is being movedin the direction towards the annular space 18, and little resistance forthe collar 25, 26 which is simultaneously being moved in the directionfrom the annular space 18. A collar 25, 26 which is in the annular space18, provides little flow resistance independently of the direction ofmotion, as liquid may pass outside the collar. If the sleeve 12 issubjected to a downward force which is greater than the force from thespring 9, the sleeve 12 (and thereby the slide 3) will move slowlydownwards because of the flow resistance in the channel 27 in the collar25. When the collar 25 enters the annular space 18, the flow resistanceis reduced, and the sleeve 12 is quickly moved to a lower end-position,in which the lower collar 26 abuts the shoulder 14, as the check valve30 will open for the liquid flow. If the downward force is removed, thespring 9 will seek to bring the sleeve 12 and the slide 3 back into theupper position. The check valve 30 will then close, and the speed of thesleeve 12 is restricted by the flow resistance in the channel 28. Thechannels 27, 28 serve as flow resistors. The check valve 29 in the uppercollar 25 will open for liquid flow, so that there will be little flowresistance when the collar 25 is displaced in the annular space 17. Whenthe collar 26 enters the annular space 18, the flow resistance isreduced, and the sleeve 12 is quickly displaced towards the upperend-position.

An axially displaceable tubular valve body 31 encloses the lower part ofthe slide 3, so that the seals 4, 5, 6 form a sliding tightening againstthe inner surface of the valve body 31. The seals 4, 5, 6 thus define anupper annular space 32 and a lower annular space 33 between the slide 3and the valve body 31, and thereby liquid cannot flow directly throughthe valve body 31. In the side wall of the valve body 31, above the areaof the seal 4, are arranged gates 34, 35, so that liquid flowing intothe upper end of the valve body 31, may flow through the gates 34 and 35out into an annular space 36 between the valve body 31 and the housing2. Further, in the side wall of the valve body 31, below the area of theseal 4, are arranged further gates 37, 38, so that liquid may flow fromthe annular space 36 into the annular space 32 or the annular space 33,depending on the position of the slide 3 relative to the valve body 31.A pre-tensioned spring 39, resting on the shoulder 41 inside the housing2, works against the underside of an external shoulder 42 on the valvebody 31, retaining the latter in an upper starting position.

Below the gates 37, 38, the valve body 31 is provided with a flowrestriction 42′ in the form of an increased outer diameter, which limitsthe cross-section of the annular space 36 at the lower end of the valvebody 31. At the flow restriction 42′ the valve body 31 is provided withexternal ribs 43 slidably resting on the housing 2, see FIG. 4.

The lower end of the valve body 31 is provided with a seal surface 44arranged to be capable of tightening against a valve seat 45 in thehousing 2, when the valve body 31 is displaced to a lower position.

When both the slide 3 and the valve body 31 are in the startingposition, the annular space 33 communicates with the annular space 36through the gates 37, 38, as is shown in FIG. 1.

Liquid may flow into the upper end of the valve device 1, down throughthe sleeve 12, through the openings 13, into the valve body 31 at theupper end thereof, through the gates 34, 35, out into the annular space36, past the flow restriction 42′, further past the seal surface 44 andvalve seat 45, out through the lower part of the valve device 1.

If the flow rate is increased, the flow restriction 42′ will cause sucha great pressure fall that a resulting force working on the valve body31, will overcome the force from the spring 39 and displace the valvebody 31 to a lower position, in which its sealing surface 44 sealsagainst the valve seat 45, see FIG. 2.

The liquid flow through the valve device 1 comes to a stop, whichresults in a pressure rise in the liquid above the valve seat 45. Anincreasing pressure difference from the upper side to the underside ofthe valve seat 45 is caused, and this effects an increasing downwardforce which works on the valve body 31 and retains the seal surface 44against the valve seat 45. It also effects an increasing downward forceworking on the slide 3. When the resulting force against the slide 3exceeds the force from the spring 9, the slide 3 is displaced downwards,and the sleeve 12 is brought along.

At the beginning the slide 3 will be displaced slowly downwards becauseof the flow resistance when the collar 25 is displaced downwards in theannular space 17. After some time, greatly determined by thecross-section of the channel 27 and the length of the annular space 17,the collar 25 enters the annular space 18. The sleeve 12 and the slide 3is then displaced quickly towards a lower position, as alreadyexplained.

As a consequence of the slide 3 being displaced downwards in the valvebody 31, communication between the annular space 36 and the annularspace 32 is established through the channels 37, 38, see FIG. 3. Liquidmay then flow from the annular space 36 to the annular space 32 andfurther through the bore 8 and the channel 7 out through the lower partof the valve device 1.

The liquid flow established entails a pressure fall on the upper side ofthe valve seat 45, and the spring 39 will, after a short while, lift thevalve body 31, so that it does not tighten against the valve seat 45.

Thereby, liquid may flow past the flow restriction 42 as well as throughthe gates 37, 38, the bore 8 and the channel 7, and the pressure may beequalized in the valve device 1.

The spring 9 seeks to lift the sleeve 12 and the slide 3 to the upperstarting position, but the flow resistance of the collar 26 in theannular space 19 makes this happen slowly. After a while, which isgreatly determined by the cross-section of the channel 28 and the lengthof the annular space 19, the collar 26 enters the annular space 18. Theflow resistance is reduced as liquid may pass outside the collar 26, andthe spring 9 quickly brings the sleeve 12 and the slide 3 to the upperstarting position, see FIG. 1.

The process is periodically repeated as long as a sufficiently greatliquid flow is being pressed through the valve device 1.

The collars 25, 26 with channels 27, 28, check valves 29, 30 and theannular spaces 17, 18, 19, filled with liquid, constitute a dampingdevice limiting the speed of the valve body 31 during part of themovement of the valve body 31.

An alternative embodiment of a damping device is described in thefollowing with reference to FIG. 5, in which reference numerals ofvalues exceeding one hundred are used, and so that components having thesame or corresponding functions as those of the damping device alreadydescribed, have been given the same reference numerals plus one hundred.Thus, in FIG. 5, is shown a part of a tubular housing 102, correspondingto the housing 2, and in which the upper part of a slide 103,corresponding to the slide 3, is shown. The slide 103 is kept in anupper starting position by a pre-tensioned spring 109 which rests on anannular shoulder 110 inside the housing 102 and works against theunderside of a plate 111 attached to the slide 103 at the upper endthereof. Liquid may pass the plate 111 through openings 113 in the plate111.

Below the shoulder 110 there is provided in the housing 102 a concentricfixed sleeve 112. There is a clearance between the housing 102 and thesleeve 112, external radial lugs or ribs 112′ supporting the sleeve 112internally in the housing 102, so that liquid may pass outside thesleeve 112.

The slide 103 runs through the sleeve 112 which is open at its upperend. In the sleeve 112 is arranged a shoulder 114 with a seal 115 whichslidingly tightens against the slide 103. At the lower end of the sleeve112 is arranged a seal 116 with also tightens slidingly against theslide 103. The seals 115, 116 define an upper annular space 117, acentral annular space 118 and a lower annular space 119 between theslide 103 and the sleeve 112. At the central annular space 118 thesleeve 112 has a larger internal diameter than at the adjacent annularspaces 117, 119. The sleeve 112 may have the same internal diameter atthe annular space 117 as at the annular space 119.

Above the shoulder 114, in the sleeve 112 there is an annular piston 120with seals 121, 122 slidingly tightening against the sleeve 112 and theslide 103, respectively. The underside of the piston 120 and the upperside of the shoulder 114 thus define a portion 123 of the annular spacebetween the slide 103 and the sleeve 112. A channel 124 in the shoulder114 connects the portion 123 of the annular space to the annular spaces117, 118, 119 below the shoulder 114. The annular spaces 117, 118, 119and the annular space portion 123 are filled with hydraulic oil oranother liquid. The upper side of the piston 120 is exposed to theliquid conveyed in the valve device 1, and ensures that always the samepressure prevails in the liquid in the annular spaces 117, 118, 119 and123 as in the rest of the valve device. The annular space portion 123serves as reservoir and pressure accumulator for liquid in the annularspaces 117, 118, 119.

The slide 103 is externally provided with a fixed upper collar 125 and afixed lower collar 126 located between the seals 115, 116. The diameterof the upper collar 125 is adapted to the annular space 117, and thediameter of the lower collar 126 is adapted to the annular space 119, sothat there is little clearance between the sleeve 112 and the collars125, 126. The distance between the collars 125, 126 is such that theymay be brought, separately or simultaneously, into the central annularspace 118 through axial displacement of the slide 103. When the collars125, 126 are in the annular space 118, there will be larger clearancebetween the sleeve 112 and the collars 125, 126 than when the collars125, 126 are in the annular space 117, 119.

In each of the collars 125, 126 is provided, in the form of a relativelynarrow channel 127 and 128, respectively, a limited cross-section by wayof which liquid may flow through or past the collars 125, 126 when theseare moved in the annular space 117 and 119, respectively. The channels127, 128 serve as flow restrictors. In each of the collars 125, 126 isfurther provided a check valve 129 and 130, respectively, of a largercross-sections than the channels 127, 128. The flow resistance past thecollars 125, 126 is thus direction dependent when the collars 125, 126are in the annular space 117 and 119, respectively. When the slide isforced downwards by the pressure created when the valve body 31 closes,the annular spaces 117, 118, 119 filled with liquid, the collars 125,126 with channels 127, 128 and check valves 129, 130, will delay themovement of the slide 103 in a manner corresponding to that explainedfor the annular spaces 17, 18, 19 and the collars 25, 26 with channels27, 28 and check valves 29, 30.

What is claimed is:
 1. A device for overcoming friction and applyingimpact energy to an object stuck within an oil or gas well, in order toloosen and disengage said stuck object through the application ofpressure changes to a liquid flowing within the bore of a coilabletubing or a drill string, and wherein a valve body is adapted to sealagainst a valve seat and shut off the liquid flow whenever the flow rateexceeds a predetermined value, thus giving rise to a build-up ofpressure in the liquid flow, until a pressure fall is caused upstream ofthe valve body, said valve body further is adapted to maintain theclosed position thereof, shutting off the liquid flow, when the flowrate exceeds a predetermined value, and that the valve body is assigneda slide adapted to open for a liquid stream past the valve body, inorder to reduce the pressure in the liquid upstream of the valve body,whenever the pressure in the liquid upstream of the valve body exceeds apredetermined value, and wherein a part of the valve body is assigned adamping device, restricting the speed of the valve body during part ofthe movements thereof from opened to closed and from closed to openedposition, and wherein the damping device comprises at least one pistonin the form of a collar providing resistance against being moved withinan annular space filled with liquid, said collar being provided with aflow resistor in the form of a channel.
 2. A device as claimed in claim1, wherein the collar is provided with a check valve which for one flowdirection allows liquid flow parallel to the liquid flow in the channel.